Raman Spectroscopy Study Of Graphene Superlattice And Hydrogenation Of Graphene

Graphene is a rapidly rising two-dimensional material with high carrier mobility, transparency, thermal conductivity, mechanical strength, specific surface area and etc. Raman spectroscopy as the basic study tool of graphene could be used to determine its layer number, probe crystal structure, type of defect, electron/hole doping, edge chirality, electronic band structure, phonon dispersion, electron phonon coupling and etc. In this thesis, Raman spectroscopy is used to probe electronic structure of 2+2 rotated tetralayer graphene superlattice(RTLGS) as well as investigate hydrogenation of graphene on different substrates. Our study facilitates the understanding of rotation angle dependent electronic properties of tetralayer graphene superlattice. The understanding of hydrogenation of graphene on different substrates will provide guidance for future application of graphene in electronic and optoelectronic devices.Besides the description of the background and technology of fabrication and characterization of graphene in the first two chapters. We focus on the systematic Raman study of band structure in 2+2 rotated tetralayer graphene superlattice(RTLGS) in the third chapter. Bernal stacking BLG are fabricated by mechanical exfoliation method and some of the Bernal stacking BLG samples are unintentionally self-folded during fabrication, and then RTLGS samples are obtained. In RTLGS, Bernal stacking BLG is sitting on top of another Bernal stacking BLG. Top two layers rotate an angel relative to bottom two layers. The mismatch between top two layers and bottom two layers gives rise to a periodic superlattice. It is found that for RTLGS, line shapes of 2D peak and 2D’ peak are similar to those of Bernal stacked BLG, which can be fitted as 4 subpeaks and 2 subpeaks, individually. However, blue shifts of those subpeaks are observed in RTLGS. It is found that frequencies of RTLGS 2D and 2D’ peaks show rotation angle dependent trends. We propose a simplified electronic band structure for RTLGS. The electronic structures of RTLGS samples are then probed from resonant Raman studies of 2D and 2D’ peak using different laser lines, some electronic states in RTLGS samples are given. Our study facilitates the understanding of rotation angle dependent electronic properties of tetralayer graphene superlattice.There is no band gap in graphene which limits its application in electronic devices and recently it is found that hydrogenation of graphene can induce a band gap. Experimentally, hydrogenation of graphene has been carried out for graphene transferred on Au, Si O2 as well as for graphene grown on Si C and transition metals. The hydrogenation of graphene on flexible substrates hasn’t been fully studied and understanding of effect of substrate’ s flexibility on hydrogenation of graphene will help in graphene based flexible electronics. Raman spectroscopy is used to monitor hydrogenation of graphene on polydimethylsiloxane(PDMS) as well as on Si O2/Si substrates. It is found that hydrogenation of graphene on Si O2/Si is much more feasiblethan those on PDMS. For graphene on PDMS substrates, hydrogenation of graphene is favored on very flexible substrates. The substrate(Si O2/Si and PDMS) and flexibility(PDMS with different flexibility) dependent hydrogenation behavior can be understood by different interactions between graphene and substrate. From this work it is found that for graphene on flexible substrate, in order to facilitate hydrogenation process, avoiding prestrain on graphene layer during growth and transfer process is highly demanded.